This invention relates to a device for joining textile yarns by compressed air without forming a knot, and relates in particular to the joining head of such a device which contains the chamber in which the joining process is carried out, and the cover which during the joining process closes the slot through which the yarns are inserted into the chamber.
Pneumatic joining of textile yarns with the aid of compressed air jets acting within the chamber is a method which has been known for a long time and which during the course of time has undergone considerable development.
Initially the yarns originating from opposite sides of the joining chamber and inserted into it through its insertion slot with their ends retained on the outside of the chamber by suitable retention devices were subjected within the chamber to the direct action of at least one compressed air jet fed generally into the centre of the chamber in order to mix and interlace the fibres under the effect of strong turbulence. Examples of joining devices of this type are described in U.S. Pat. No. 3,461,661 and in German patents 27 50 913 and 28 56 514.
The need to improve interlacing between the fibres by removing the original yarn twist led to methods such as those described in German patents 30 04 721 and 30 40 661 and in European patent 41 818 which, although using different types of pneumatic joining devices have the common concept of inducing untwisting of the ends of the yarns to be joined. Thus German patent 30 04 721 describes a device comprising two separate chambers axially spaced apart in which, if viewed in the same axial direction, a clockwise-rotating air swirl is created in one chamber and an anticlockwise-rotating air swirl is created in the other chamber to untwist the free ends of the yarns to be joined. In German patent 30 40 661 the same result is obtained by a joining device in which the two opposing air swirls are created within a single chamber symmetrical both about a transverse central plane and about a longitudinal central plane. An analogous method, described in European patent 41 818 comprises a joining chamber consisting of two partially touching parallel parts with a common longitudinal slot for introducing the yarns, in which, if viewed in the same direction, a substantially clockwise-rotating air swirl is created in one chamber and a substantially anticlockwise-rotating air swirl is created in the other chamber.
The further development of pneumatic joining devices involved preceding the actual yarn joining operation by a preliminary stage in which their ends were treated to untwist these ends and to open and parallelize the fibres in them. It has consequently been suggested to use chambers arranged to twist rather than untwist the yarns during the operation by the use of air swirls operating in the same direction as the original twist in the yarns to be joined. Examples of joining chambers of this type are described in Italian patent 1,137,713, in Italian utility model 205,142 and in German patents 30 49 426, 34 18 396 and 36 26 374.
There remained the problem of possible mutual negative influence of the two opposing air swirls, generated by nozzles opening into the chamber in positions very close together, this problem having been solved by a method described in German patent 35 40 324, by which the chamber is divided into two parts by a central transverse air bleed fissure between the two nozzles, which open into the two parts of the chamber respectively, so as to create opposing air swirls within said parts. This transverse fissure also results in a reduction in the quantity of air laterally emerging from the respective ends or lateral ports of the chamber.
In this respect, it has been found that a large quantity of air escaping from the lateral ports of the chamber can damage the yarn fibres, especially of soft twist or very short fibre yarns.
Although this latter method is very valid and has given excellent results, it still has certain drawbacks in that after cutting the yarn ends they lie freely within the two parts of the chamber without having a precise position, so that the yarn ends are able to assume poorly defined positions and can be struck by the opposing air swirls in a not always identical manner within the two parts of the chamber. The joints obtained with such a chamber can consequently show undesirable non-uniformity.